[Premium-Rx] WJ8711A DYNAMIC RANGE & Ip3

[Marco IK1ODO -2]

Hello Pat,

welcome to the world of measuring A/D converters and DSP receivers :-)

I never measured the HF1000, and I don't know the exact architecture 
of the radio, but I understand that final selectivity is done at 25 
kHz IF by digitizing the IF at 100 kS/s and then by DSP.
A/D converters have non-linearities that are very different from an 
anogic mixer/IF strip/demodulator. In particular, IMD3 signals do not 
decrease with the law that you may expect. There have been detailed 
discussion in QEX, and you may have a look at 
http://www.sm5bsz.com/dynrange/intermod.htm

Compare this with your findigs, may be that you see similarities. I 
did several IM3 tests on direct sampling HF receivers (SDR-IQ, 
Perseus, HPSDR, QS1R) and I have been able to see the analog IM3 
products only close to the A/D converter saturation point. At lower 
levels the quantization noise and other problems prevail (typically 
it seems that digital noise from outpuut lines of the ADC couples to 
the input).
There has been also some interesting messages on the argument by Andy 
G4JNT on the rsgb_lf_group. If you don't have access to it, let me know.

73 - Marco IK1ODO


At 11:08 01-11-10, you wrote:
>Hello to all,
>
>Can anyone who has measured the true dynamic range and Ip3 of an WJ
>8711/A/HF1000 DSP HF Receiver let me know how they managed to do it  please.
>
>Two receivers were in here for measurement yesterday.
>
>  Using a signal spacing of 20kHz with max levels of -10dBm I  could not get
>any meaningful results using the "ARRL" (by N1UL) method for  measurement
>which always works without fail.
>
>The test equipment is not questionable, it performed flawlessly  on other
>Racal, R&S and AEG analogue receivers here  under exactly the same
>measurement conditions.
>
>What point am I missing? What am I doing wrong?
>
>Thanks and regards,
>
>Pat G3YFK
>
>ps:  Apologies but I always ask when I do not  know!